Vented mold and method for producing molded article

ABSTRACT

The invention relates mold, particularly a mold for producing foam articles. In a preferred embodiment, the mold comprises a lid and a bowl releasingly engageable to define a mold cavity, the lid comprising: (i) a vent having a passageway for gas to escape from the mold cavity, and (ii) a plurality of grooves connected to the vent. The use of a plurality of grooves/slots in the mold cavity surface effectively acts as a siphon to draw gas away from the composition to be molded. The plurality of grooves/slots is connected to one or more vents which then allows for escape of the gas from the mold cavity to the exterior of the mold.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a divisional application claiming the benefitunder 35 U.S.C. §120 of U.S. patent application Ser. No. 12/335,312,filed Dec. 15, 2008, which claims the benefit of U.S. patent applicationSer. No. 10/973,985, filed Oct. 27, 2004, now U.S. Pat. No. 7,481,637,which claims the benefit under 35 U.S.C. §119(e) of provisional PatentApplication Ser. No. 60/570,075, filed May 12, 2004, the contents of allare incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a vented mold and to a method forproducing a molded article.

2. Description of the Prior Art

Many articles are manufactured by placing a raw material into a cavityin a mold wherein the raw material undergoes a physical change (e.g., itexpands or foams) and the article produced thus acquires the shape ofthe cavity. In particular, this technique is commonly employed forproducing foamed articles made from polymeric foams such as polyurethanefoam, latex (e.g., natural and styrene-butadiene rubber) foam and thelike.

For example, automotive seats are commonly manufactured frompolyurethane cushions which are molded to shape and then covered with avinyl, cloth or leather finish cover (also known as a “trim cover”).Polyurethane foams are somewhat unique in that foaming and at least aportion of the polymerization process occur simultaneously. Thus, in theproduction of polyurethane foam using, for example, a conventional coldfoam technique, a typical formulation comprises:

-   -   1. Polyol    -   2. Water    -   3. Tetramethyl ethane diamine    -   4. Dimethyl ethanol amine    -   5. Polyisocyanate

The mixture is dispensed into a mold using a suitable mixing head, afterwhich the mold is then closed to permit the expanding mass within it tobe molded. Accordingly, it is convenient generally to refer to themixture initially dispensed into the mold as “a liquid foamablepolymeric composition” or, in this case, “a liquid foamable polyurethanecomposition”. As the composition expands in the mold, polymerizationoccurs and the polymer so formed becomes solidified.

When molding a liquid foamable polymeric composition to form articles,such as polyurethane foam articles, it is conventional to use aclam-shell mold comprising a bottom mold and a top mold which, whenclosed, define a mold cavity. The mold is opened, the liquid foamablepolyurethane composition is dispensed into the mold cavity and the moldis closed as a chemical reaction causes the composition to expand. Afterthe mold is closed, the composition expands to fill the interior cavityof the mold. Alternatively, the composition may be dispensed into aclosed mold. In either case, as the polymerization reaction iscompleted, the foam cures and permanently assumes the shape of the moldcavity.

As is known to those of skill in the art, it is important during thisprocess that the mold be adequately vented to allow the air present inthe mold to exit the mold as the foamable composition expands. Further,it is important to allow a portion of the gases (typically CO₂ in theproduction of polyurethane) generated during polymerization to exit themold.

Failure to adequately vent the mold results in defective molded articlesexhibiting symptoms of improper foaming such as surface hardening (orfoam densification) and/or void formation in the finished article due totrapped gas or air bubbles. At the other extreme, excess venting of themold will also result in defective molded articles due to collapse ofthe foam prior to curing; this phenomenon is often referred to as the‘soufflé’ effect. Thus, proper venting of a mold is an important factorin producing molded articles of acceptable quality.

Typically, first generation clam-shell molds have been designed withdrilled or cut passages in the top mold to provide vents. Locating,sizing and deciding upon the number of these vents is a matter of someskill on the part of mold designer and the production engineers, and isoften an iterative procedure with more vents being added to variouslocations or other vents being blocked-off after test runs have beenmade.

During molding operations some liquid foamable polymeric compositionwhich moves into the vent is wasted. It is generally desired to minimizethe amount of wasted material (also known as “flash”, “mushrooms”,“buds”, “pancakes” and the like) for two reasons, namely (1) the wastedmaterial adds to the overall expense of chemicals required to producethe finished article, and (2) the wasted material must be removed fromthe molded article prior to the finish cover being applied, therebynecessitating additional labour and the costs associated therewith.

As will be developed below, improvements to venting during such moldingoperations have advanced the art to a certain degree. However, molddesigners and production engineers are continually striving to optimizethe compromise between providing enough venting at the proper locationswhile avoiding excess venting and minimizing material wastage duringventing and the number of vents needed to achieve adequate venting ofthe mold cavity. Further, as will be developed below, notwithstandingadvances in the art pertaining to venting, there is still a problem withmolded articles, particularly those made of polyurethane foam.Specifically, there is the problem of foam collapse (referred to above)and with voids and/or underfill which will be described in more detailbelow. Thus, there is an ongoing need in the art to improve ventingtechniques to solve the problem of foam collapse, voids and/orunderfill.

SUMMARY OF THE INVENTION

It is an object of the present invention to obviate or mitigate at leastone of the above-mentioned disadvantages of the prior art.

Accordingly, in one of its aspects, the present invention provides amold for producing molded articles, the mold comprising a first mold anda second mold releasingly engageable between an open position and aclosed position, the closed position defining a mold cavity, a surfaceof the mold cavity comprising at least one groove connected to at leastone vent, the at least one vent comprising a passageway for gas toescape from the mold cavity.

In another of its aspects, the present invention provides a mold forproducing molded articles, the mold comprising a lid and a bowlreleasingly engageable to define a mold cavity, the lid comprising: (i)a vent having a passageway for gas to escape from the mold cavity, and(ii) a plurality of grooves connected to the vent.

In yet another of its aspects, the present invention provides a devicefor producing molded articles, the device comprising a lid and a bowlreleasingly engageable between an open position and a closed position,the closed position defining a mold cavity, at least one of the lid andthe bowl comprising: (i) a plurality of vents, each vent having apassageway for gas to escape from the mold cavity, and (ii) a pluralityof interconnected grooves arranged to be in fluid communication with theplurality of vents.

Other aspects of the present invention relate to the production of amolded part, preferably a molded foam part, using the above molds anddevice.

Thus, the present inventors have discovered a new approach to improvingventing of mold, particularly molds for production of foam articles. Theapproach is quite different from that used in the past.

The conventional approach of venting involved placement of a number ofvents in areas of a mold where it was believed localized collection ofgas would occur in the mold cavity. In many cases, placement of ventswas done in an iterative manner. Specifically, as foam parts were madeand surface defects were seen, the response would be simply to place avent (e.g., one or both of a so-called “autovent” and “ribbon vent”discussed below) in the area of the mold corresponding to the positionof the defect on the resulting foam part. The result was the provisionof a large number of vents (40 or more) at the parting line of the moldand/or in the top mold or lid of the mold. Even following this approach,the occurrence of foam collapse and voids has not been overcome and theoccurrence of underfill is only marginally better, in part due to the(wrong) assumption that the location of the defect in the final productis coterminous with the location of the gas to be vented during foamexpansion.

The approach used by the present inventors is to de-emphasize locationof a great number vents in potential areas of concern in the mold.Rather, the present inventors have discovered that the use of one ormore grooves/slots in the mold cavity surface effectively acts as asiphon to draw gas away from the composition to be molded. The at leastone groove and/or slot is connected to one or more vents which thenallows for escape of the gas from the mold cavity to the exterior of themold.

In a highly preferred embodiment, the one or more grooves/slots areprovided in a so-called network or grid-like orientation to cover asubstantial portion of the surface of the mold cavity as a web (e.g., asubstantial portion of the surface of the mold cavity corresponding tothe B-surface of the finished part). This allows for the use ofsignificantly fewer vents and for de-emphasis on precise location of thevents in each potential area of concern in the mold cavity. Equally ormore importantly, the provision of such a groove and/or slot, preferablyin the network or grid-like fashion described herein, results in thesignificant advantage of production of molded articles that are free ofthe problem of foam collapse, voids and/or underfill.

A number of other advantages accrue from the use of one or moregrooves/slots in the mold cavity surface effectively as a siphon to drawgas away from the composition to be molded and to channel this gas toone or more vents. These advantages include:

-   -   It is possible to produce foam parts having relatively low        density while obviating and/or mitigating the risk of occurrence        of foam collapse. Previously, one approach to manage the risk        was to design the chemistry of the foamable composition to        result in a relatively high density product. The potential to        produce relatively low density products using the venting        approach described herein would result in lighter weight        products—this would be highly advantageous in vehicular        applications given the increasing cost of fuel.    -   It is possible to introduce heterogeneous elements to the        composition to be molded while obviating and/or mitigating the        risk of occurrence of foam collapse. For example, if a liquid        foamable composition is dispensed in the mold cavity, the        heterogeneous element might be one or more of a foam insert        element (e.g., to produce a dual-hardness/firmness or        multiple-hardness/firmness foam product) or a non-foam insert        (e.g., a portion of a touch fastener system (also know as a        Velcro™ fastener), a mechanical clip, a cloth insert and the        like). Previously, the nature, size and/or position of such a        heterogeneous element has been relatively limited owing to the        risk of foam collapse.    -   It is possible to solve collectively the problems of foam        collapse and the occurrence of underfill and voids in the foam        product.    -   It is possible to significantly reduce the number of vents need        to achieve adequate venting of the mold. This provides savings        in capital costs and in maintenance. Further, the ability to use        significantly fewer vents creates a predictable environment        around the vents (and the mold). This creates the potential to        manage the environment around the vents (and the mold) in a        manner which obviates and/or mitigates uncontrolled release gas        from the mold.    -   The one or more grooves/slots in the mold cavity surface are        effectively self-cleaning in that, after gases are vented from        the mold, the mold cavity is filled and the resulting product is        demolded with a “negative” of the one or more grooves/slots        (e.g., in the form of one or more ridges). There is little or no        fouling of grooves/slots either by the moldable composition        and/or by any mold release agents initially sprayed on the mold        cavity surfaces to facilitate demolding. Avoiding fouling by        mold release agents is particularly advantageous since such        agents are regularly used in the art and would be expected to be        applied to the one or more grooves/slots.

The use of one or more grooves/slots is active for siphoning orotherwise channeling gas (e.g., via a capillary effect) in the moldcavity as the internal pressure in the mold remains relatively low. Thegrooves and/or slots are connected to a vent which maybe a ribbon vent,an autovent or a so-called smart vent.

It is preferred to have the one or more grooves/slots disposed in a“high point” of the lid of the mold since this will facilitate drawingof the gas from the top of the geometric feature which is to be vented.It also highly preferred to orient a slot/groove on the periphery of themold cavity near the parting line. This peripheral groove/slot can bedisposed in the lid or the bowl of the mold and depends, in part, of theshape of the article being produced.

The approach of using grooves/slots is particularly applicable in asituation where the part to be molded is highly contoured. Thus, thegroove/slot maybe disposed on the high point of a contour surface asdiscussed above and/or the tangent of radius of the edge or lip of acontour in the mold.

When a peripheral groove/slot is used as described above, it ispreferred to include one or more so-called connection grooves/slots tointerconnect the peripheral groove/slot with, for example, a ribbonvent.

For the surfaces of the mold cavity that are relatively flat, it ispreferred to orient a number of grooves/slots in a network or grid-likefashion to provide a substantial checkerboard arrangement ofgrooves/slots with each square in the checkerboard having an area in therange of from about 4 in² to about 16 in². Of course, where the majorsurface of the mold cavity is slightly contoured, the grid may notnecessarily need to contain grooves/slots arranged to define precisesquares.

In the event that the part to be produced is somewhat elongate, it ispreferred to run a number of grooves/slots lengthwise on the surface ofthe mold cavity and couple this with pour pattern generally at one endof the mold cavity. By dispensing the foam composition at one end of themold cavity, the foam needs to travel lengthwise to fill the mold cavityand this allows lengthwise orientation of the grooves/slots to run aheadof foam flow reliably moving gas from the mold cavity to the vent andout of the mold.

As will be discussed below, it is possible to have one or more “mini” orisolated networks or grid-like orientation of grooves/slots to deal withhighly contoured or raised sections of the mold cavity.

It is also highly preferred to have one or more groove/slots oriented ina manner whereby the groove/slots have redundant paths to a number ofvents disposed in the lid and/or parting line of the mold.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will be described with reference tothe accompanying drawings, wherein like reference numerals denote likeparts, and in which:

FIG. 1 illustrates a sectional view of a prior art mold;

FIG. 2 illustrates a sectional view of a foam product made using themold illustrated in FIG. 1;

FIGS. 3 and 4 illustrated an enlarged perspective view of a portion of aprior art vent device;

FIGS. 5 and 6 illustrate production of a molded article in a prior artmold;

FIG. 7 illustrates a perspective view of a foam article made using theprior art mold illustrated in FIGS. 5 and 6;

FIG. 8 illustrates a sectional view of a preferred embodiment of thepresent mold shown during production of a molded article;

FIG. 9 illustrates a top view of the mold illustrated in FIG. 8,partially ghosted to show the contents of the mold;

FIG. 10 illustrates a perspective view of the foam article made usingthe mold illustrated in FIGS. 8 and 9;

FIG. 11 illustrates an enlarged sectional view of a modification of themold illustrated in FIG. 8;

FIG. 12 illustrates an enlarged portion of a foam product made using themold illustrated in FIG. 11;

FIGS. 13-16 illustrate various foam articles made according tovariations in the network of grooves made to the present mold;

FIG. 17 illustrates an enlarged sectional view of another embodiment ofthe present mold;

FIG. 18 illustrates an enlarged view a foam product made using the moldillustrated in FIG. 17;

FIG. 19 is an enlarged perspective view of installation of a vent in thepresent mold;

FIG. 20 illustrates an enlarged sectional view of a vent in the presentmold;

FIG. 21 illustrates an enlarged perspective view of a first preferredvent installed in the present mold;

FIG. 22 is a sectional view along line XXII-XXII in FIG. 21;

FIG. 23 illustrates an enlarged perspective view of a second preferredvent in FIG. 20 installed in the present mold;

FIG. 24 illustrates a sectional view along line XXIV-XXIV in FIG. 23;

FIGS. 25-28 illustrate operation of the vent shown in FIGS. 21-22; and

FIG. 29 illustrates an enlarged perspective view of a foam product madeusing the vents illustrated in FIGS. 20-28.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The most preferred liquid foamable polymeric composition is based uponpolyurethane, which will be referred throughout this specification.However, it will be apparent to those of skill in the art that thepresent invention is applicable to other types of molding operationsincluding, but not limited to, latex foam, neoprene foam, PVC foams andthe like.

A first generation prior art mold will first be discussed, withreference to FIGS. 1 and 2, and a second generation prior art mold willthen be discussed, with reference to FIGS. 3 and 4.

With reference to FIGS. 1 and 2, a typical clam-shell mold, similar tothose used for forming an automotive seat cushion from polyurethanefoam, is indicated generally at 20 in FIG. 1. Mold 20 includes a lowermold 24 (also known in the art as a “bowl”) and an upper mold 28 (alsoknown in the art as a “lid”) which are joined by a conventional hinge orother means (not shown). Lower mold 24 and upper mold 28, when closed,define a cavity 32 which corresponds to the shape of the automotive seatcushion.

In use, upper mold 28 is released from lower mold 24 and apre-determined amount of liquid foamable polyurethane composition isdispensed into lower mold 24. Upper mold 28 and lower mold 24 are closedand engaged to seal the mold, and the liquid foamable polyurethanecomposition expands, displacing the air within cavity 32. This displacedair exits cavity 32 through a relatively large parting line vent 36 andthrough one or more top vent passages 38 in upper mold 28. Further, asthe polyurethane composition expands, polymerization of the compositionoccurs along with the evolution of gaseous CO₂ in cavity 32. Thisgaseous CO₂ may also exit cavity 32 through parting line 36 and throughtop vent passages 38. As is well known to those of skill in the art (andbeyond the scope of this discussion), the liquid foamable polymericcomposition eventually completely polymerizes and cures, acquiring theshape of cavity 32.

As is also known to those of skill in the art, the amount of liquidfoamable polyurethane composition dispensed in cavity 32 must beselected to ensure that cavity 32 will be substantially completelyfilled, in order to avoid the occurrence of underfill-associate foamcollapse, voids and other foaming defects in the molded article. Whilethe determination of the proper amount of liquid foamable polyurethanecomposition for a particular mold may generally be calculated, whenusing a first generation mold such as mold 20, it has been required todispense an excess amount of polymeric composition into the mold tocompensate for material which moves through and exits parting line vent36 and top vent passages 38. This excess, while assisting in ensuringthat cavity 32 is filled to avoid the occurrence of underfill-associatefoam collapse, voids and other foaming defects in the molded articles,is in fact simply a wastage of valuable raw material which must belaboriously removed in a further post-production step.

In these first generation prior art molds, during the molding operation,air and the reaction gases produced from the expanding composition exitfrom cavity 32 through parting line vent 36 and top vent passages 38until the foam reaches the level of their respective entrances.

At this point, any further expansion of the foam results in movement ofthe foam into parting line vent 36 and/or top vent passages 38. In thesimplest case of a cavity without irregularities, the foam reaches thelevel of the parting line vent and/or the vent passages at approximatelythe same time, which usually occurs at or near the maximum expansionpoint of the foam. Thus, provided that the proper amount of liquidfoamable polyurethane composition has been dispensed into the cavity,only a small amount of foam enters the parting line vent and/or the ventpassages as cavity 32 is completely filled.

In practice, however, as shown in FIG. 1, most molds includeirregularities in their cavities for various features required on themolded article. In such a case, the thickness and shape of cavity 32typically varies across the cavity and the entrance to parting line vent36 and top vent passages 38 in the mold may thus be located at differentheights depending upon where they communicate with cavity 32. Further,localized areas of varying pressure also occur within cavity 32 due tothe manner in which the foam and the gases produced collect in and movebetween the irregularities therein and thus the level of expanding foammass in different parts of cavity 32 at different times may vary.

Due to the above-mentioned factors, the foam in the cavity typicallyreaches the level of the parting line vents and/or different ventpassages at different times while the foam is still expanding. Forexample, in a region wherein the top of cavity 32 is lower thansurrounding regions, such as indicated at 40 in FIG. 1, the foam mayquickly reach the top vent passages 38. As the foam is still rising inthe rest of cavity 32 and has not yet cured, a relatively significantamount of foam may enter top vent passages 38 in this region.

Again, as the amount of foam which enters parting line vents 36 and topvent passages 38 reduces the amount of foam remaining in cavity 32 by alike amount, it is necessary that the amount of liquid foamablepolyurethane composition placed in cavity 32 include an amount in excessof that required to fill cavity 32 to offset the foam which entered theparting line and vents. This excess amount, while necessary for properoperation of the prior art mold, is essentially wasted material whichmust be laboriously removed in a further post-production step and thusadds to the cost of forming the article.

Further, as shown in FIG. 2, the foam which enters top vent passages 38forms “mushrooms” 54 (shown in ghosted line) of wasted material on themolded article 50. Further, the material which enters parting line vents36 forms “pancakes” 55 of wasted material on the molded article 50.Typically, mushrooms 54 and pancakes 55 must be disconnected fromarticle 50 and removed from the mold 20 prior to application of a finishcover to ensure a finished covered article which is of acceptableappearance and texture, and to prepare mold 20 for re-use. The necessityof removing mushrooms 54 and pancakes 55 results in an increased labourcost associated with manufacturing the molded product.

In addition to the excess liquid foamable polyurethane composition whichis added to offset the material extruded into the vents, excess liquidfoamable polyurethane composition is also added to compensate forprocess variations due to changes in temperature, humidity, ambientpressure and minor changes in the composition of the liquid foamablepolyurethane composition. Accordingly, in these first generation priorart molds, the wastage of material exiting the vents is inevitable.

In U.S. Pat. Nos. 5,356,580 (Re. 36,413), 5,482,721 (Re. 36,572) and5,587,183 [collectively referred to as “the Clark et al. patents”],there is disclosed a second generation mold. The second generation moldtaught by the Clark et al. patents replaces parting line vents 36 inFIG. 1 described hereinabove with improved parting line vents. Theseimproved parting line vents are highly efficient vents that achieve thebulk of venting of the mold cavity. The second generation mold taught bythe Clark et al. patents replaces top vent passages 38 of FIG. 1described hereinabove with an improved top vent system. As is known inthe art, top vent systems are needed to vent isolated regions (i.e.,from the parting line vents) of the mold cavity. With references toFIGS. 3 and 4 hereof, a discussion of the operation this improved topvent system second generation mold will follow.

With reference to FIGS. 3 and 4, a top vent system 60 is illustrated.Top vent system 60 comprises a cylindrical bore 62 and a relief pin 64disposed within cylindrical bore 62. The exterior of cylindrical bore 62comprises a threaded portion 66 which engages a complementary threadedportion of the mold (not shown). In the illustrated embodiment, theportion of relief pin 64 nearest the opening of cylindrical bore 62 ishexagonal in cross-section. The six points of the hexagonalcross-section of relief pin 64 are in engagement with cylindrical bore62 and define six segment-shaped vent passages 68. The proximal end (notshown) of relief pin 64 comprises a cross-section complementary tocylindrical bore 62. An opening (not shown) is provided between thedistal end and the proximal end (not shown) of relief pin 64 to allowgases entering vent passages 68 to exit top vent system 60.

Top vent system 60 is incorporated in a mold such as mold 20 (FIG. 1)where it would replace each of vent passages 38. In use, liquid foamablepolyurethane composition is dispensed into cavity 32, and lower mold 24and upper mold 28 are sealingly engaged. The air in cavity 32 and thegases produced by the chemical reaction occurring in the expandingcomposition are vented through vent passages 68. The viscosity of thesegases are such that they flow relatively easily through vent passages68. Once the level of foam in mold 20 reaches the entrance to ventpassages 68, the foam enters vent passages 68. Due to the presentationof a restriction by vent passages 68 to the expanding composition, thelatter can only move slowly through vent passages 68. Provided that thethickness of vent passages 68 has been properly selected, the liquidfoamable polymeric composition will stop moving therein before ittravels a significant distance along the vents and before it the exitopening (not shown) of top vent system 60.

Once expansion of the foaming mass is complete, the foam articleproduced is demolded from mold 20. This is achieved by opening lowermold 24 and upper mold 28 and removing the foam article from lower mold24. During mold opening, any foam material which has expanded in ventpassages 68 will be torn from the foam article. Such torn materialresults in blockage of vent passages 68 and thus, must be removed priorto reuse of mold 20. This is achieved by sliding relief pin 64 towardand extending it out of the distal end of cylindrical bore 62 (FIG. 4).As described in the Clark et al. patents, this sliding operation resultsin the proximal end (not shown) of relief pin 64 (i.e., having across-section complementary to cylindrical bore 62) sweeping out ofcylindrical bore 62 any foam material blocking vent passages 68.

With reference to FIGS. 5-6, there is illustrated operation of a mold100 similar to that taught by the Clark et. al patents. Thus, mold 100comprises a lid 105 and bowl 110 which is realisably engageable with lid105. Lid 105 includes a series of parting line or so-called “ribbonvents” disposed therein.

Also disposed in lid 105 are a series of so-called autovents 120 similarto those taught by the Clark et. al patents.

In use, a foamable composition (not shown) is disposed in bowl 110 via adispenser 125. Lid 105 is then closed and the flowing mass is allowed tofill the mold cavity. Thereafter, lid 105 is swung open and a foam part130 is removed from mold 100. Foam part 130 comprises a series of foamribbons 135 which need not be trimmed and can simply be folded backduring application of a trim cover to form part 130.

Despite the advances made in the art by the teachings in the Clark et.al patents, there are situations where the quality of the product isless then desirable.

Specifically, as discussed above, there are two defects which are seenfrom time to time: voids and underfill. Underfill is a surfacephenomenon which manifests itself in foam product 130 in the form ofsurface cavities 140. Further, the formation of voids 145 within foamelement 130 (“subsurface voids”) and on the surface of foam element 130(not shown—“surface voids”) is another problem. Surface voids tend to bemanifested in the foam product as a localized area of the foam part thathas not been formed—e.g., the foam composition does not expand tocompletely occupy a highly contoured section of the mold lid such thatthe resulting foam part is missing a section corresponding to the void.In conventional molding techniques, lid 105 is used to mold theso-called B-surface of the foam part whereas the surface of bowl 110 isused is use to mold the so-called A-surface of foam part 130. Whilesurface cavities 140 can occur on any surface of foam element 130, theycan be regularly present under the B-surface of foam element 130. It hasbeen conventional in the art to respond to observation of underfillsurface cavities 140 by placement of another autovent 120 in the area oflid 105 corresponding to the location of void 140.

In the result, for a single mold, it has become commonplace to use onthe order of 40 (or more) vents made up of ribbon vents 115 andautovents 120 in a single mold 100. Even with provision of such a largernumber of vents, appearance of underfill surface cavities 140 and voids145 (surface voids or subsurface voids) still occurs.

The present inventors have adapted a completely different approach toimproving venting of gas formed as the foaming mass fills the moldcavity.

Specifically, the present inventors have discovered that it is notnecessary to have such a large number of vents nor is it necessary torely on such vents for venting a localized portion of the mold cavity.Thus, the present inventors have discovered that one or more grooves (orslots) in the surface of the mold cavity can be used as a conduit tofunnel, draw, siphon, etc. gas to be vented to a conventional ventwithout the need to place a vent in each area where gas is expected tobe vented.

In a highly preferred embodiment of the invention, these grooves orslots are disposed in a intersecting or a grid-like fashion combinedwith provision of at least one such groove/slot in the periphery of themold cavity. These groove/slot function as siphons (e.g. via a capillaryeffect) to facilitate removal of gas from the mold cavity.

Thus, in a preferred embodiment, the venting approach in the presentmold relates to use of previous local vents as effective area vents bydisposing a plurality of grooves/slots in the mold cavity surface. Thecapacity of these grooves/slots to transport gas effectively is afunction of the interaction with the natural growth of the rising foam,the thickness of the area in which the grooves/slots are contained andthe obstruction effect of the geometries in the path to the vents. Thus,the grooves-slots are effective for channeling gas to be vented to avent.

As will be developed further below, it is possible to connect thisnetwork or grid-like arrangement of grooves/slots to conventional ventssuch that those taught in the Clark et. al patent. The improvement is asignificant reduction in the number of vents required to achieve properventing and the ability to produce parts which are substantially free ofvoids and underfill—the provision of such parts is a particularlysignificant advantage of the present invention.

With reference to FIG. 8, there is illustrated a mold 200 comprising alid 205 and a bowl 210 which are releasably engageable in a mannersimilar to that described above with respect to mold 100. Four vents 220are disposed in lid 205. Also disposed in lid 205 is a network 225 ofgrooves. Network 225 extends to a peripheral portion 230 of the moldcavity.

As can be seen with reference to FIG. 9, network 225 is connected tovents 220.

With further reference to FIG. 8, once a liquid formable composition 235is dispensed into mold 200, composition 235 expands in the direction ofarrows A. During this process, gas is produced and the pressure in moldcavity increases. The grooves/slots in network 225 are effectivelydisposed ahead of foam flow and are reliable to channel or funnel gastoward vents 220 even though vents 220 are not disposed throughout theentire surface of lid 205. The drawing out of gasses produced duringexpansion is facilitated by placement of vents 220 at or near the peakof the contours in lid 205.

The resulting foam part 240 is shown in FIG. 10. By adopting thecombination of network 225 and vents 220, foam part 240 can be producedwith virtually no underfill or voiding. Further, as shown in FIG. 10foam part 240 comprises a “negative” of network 225 on the B-surfacethereof in the form of a network 245 of foam ridge. In essence, foampart 240 is completely trim-free and can be sent to trim coveroperations without the need to remove flash or other excess materials.

With reference to FIG. 11, there is illustrated adaptation of network225 of grooves/slots to a parting line or so-called “ribbon vent”. Inthis case, vent 220 has been replaced with a ribbon vent 222 similar tothe one described in Clark et al. patents discussed above. Further,network 225 of grooves/slots has been extended to rise to a peak 212 ofthe mold cavity.

The resulting part 242 is shown in FIG. 12 where a “negative” 227 ofnetwork 225 has been produced—i.e., the “negative” is simply a network227 of molded foam ridges which filled network 225 during expansion offoamable composition 235. As shown in FIG. 12, foam element 242comprises a series of ribbons 235 produced in ribbons vents 220.

With reference to FIGS. 13 and 14, there is illustrated sectional andenlarged sectional perspective views of a foam part 300 made inaccordance with the present mold. For ease of illustration andunderstanding, the resulting foam part is illustrated. However, those ofskill in the art will understand based on this specification that thesefoam parts were made using the network or grid-like orientation ofgroove/slots. Thus, foam part 300 comprises a lip (or raised edge) 305.As shown, network 325 of foam ridges includes a peripheral foam ridge330 connected with network 325. In this case, a series of connectingfoam ridges 332 interconnect peripheral ridge 330 to a number ribbons335. Network 325, peripheral foam ridge 330 and connecting foam ridges332 are produced by a complementary network of grooves/slots.

With reference to FIG. 15, there is illustrated a foam element 400comprising a lip portion 405 and a network 425 of ridges produced fromcomplementary grooves/slots in a mold in accordance with the presentinvention. Foam part 400 further comprises a peripheral ridge 430 formedfrom a complementary groove/slot in a mold according to the presentinvention. Foam part 400 further comprises connecting ridges 432 formedfrom complementary grooves/slots which connect to ribbon vents (notshown) in the manner discussed above. These ribbon vents result inproduction of ribbons 435 as discussed above.

The B-surface of foam part 400 comprises a raised section 440. Raisedsection 440 has a localized network 445 of ridges formed from acomplementary network of grooves/slots in the mold according to theinvention. Since network 445 is isolated from network 425, a vent (shownin ghosted outline above section 440) is used to facilitate venting ofthe mold cavity corresponding to the region defined by section 440.Provision of isolated network 445 and a separate vent allow for theproduction of raised section 440 without the occurrence of underfill orvoids—i.e., this notwithstanding the fact that raised section 440 ishighly contoured and is almost right-angled with respect to the majorportion of the B-surface of foam part 400.

Foam part 400 further comprises a raised section 450 which is shorterthan raised section 440. To achieve proper venting of the section of themold cavity corresponding to raised section 450 without the occurrenceof voids or underfill, a portion of the network of grooves/slots in themold is disposed on the portion of the mold cavity corresponding toraised portion 450 so that this portion of the mold cavity is vented viathe network of grooves/slots resulting in the production of network 425.

FIG. 16 illustrates a foam part 500 having a higher raised section 540and a lower raised section 550 similar to those shown in FIG. 15 withrespect to foam part 400. In the case of foam part 500, peripheral ridge530 and the ridges of “main” network 525 and the ridges of network 545are all interconnected thereby obviating the need for connecting ridgesand ribbons, including obviating the need for ribbon vents in the moldused to produce foam part 500. Rather, autovent vents or the like can beused at the location shown in ghosted outline shown in FIG. 16 toachieve effective area venting of the mold cavity.

FIG. 18 shows an enlarged portion of a slightly modified version ofelement 400 wherein “mini” network 447 of ridges has been slightlymodified compared to “mini” network 445 in FIG. 15.

FIG. 17 illustrates an enlarged section view of a portion of the moldused to produced element 400 shown in FIG. 18. Thus, a “main” network ofgrooves/slots is provided and is connected to a peripheral groove/slot,connected grooves/slots and ribbon vent as discussed above. Peak 212 oflid 205 is provided with a “mini” network 247 of grooves/slots which areinterconnected and isolated with respect to “main” network 225. “Mini”network 247 of grooves-slots is connected to a vent 220 as discussedabove.

Thus, in operation, gases in the main portion of the mold cavity will bevented via “main” network 225 of grooves/slots, peripheral groove/slot,connection grooves/slots and ribbon vents (all not shown in FIG. 17 butreferred to above) whereas gas that may be trapped in peak 212 will bevented via “mini” network 247 of grooves/slots and vent 220.

With reference to FIG. 20, there is shown a schematic representation ofconnection of vent 220 to lid 205 of mold 200. Thus, vent 220 comprisesa threaded portion 221. Lid 205 comprises an internally threaded portion206 which compleents threaded portion 221 of vent 220. Thus, vent 220 issimply threaded into lid 205 via threaded portions 206 and 221.

Vent 220 can take a number of different forms. Thus, with reference toFIG. 20, there is shown a large sectional view of a vent 600 disposed inlid 205. Vent 600 maybe constructed in a manner similar to vent assembly98 described in the Clark et. al patents.

With reference to FIGS. 21, 22 and 25-28, there is illustrated analternate vent 700 which may be used in place of and/or in addition toone or both of vents 220 and 600 discussed above.

Thus, vent 700 comprises a threaded section 721 which maybe engaged witha complementary threaded section (not shown) in lid 205 as discussedabove with reference to FIG. 19.

Vent 700 comprises a passageway 705 in which is disposed an obstruction710. Branching off of passageway 705 is a conduit 715. Disposed belowvent 700 is a pair of opposed sensor elements 720 (only one is shown inFIG. 21). Sensor element 720 maybe an optical sensor (e.g., infrared andthe like), an acoustical sensor, a capacitance sensor and the like.

The operation of vent 700 will now be discussed with reference to FIGS.25-28.

Thus, a liquid foamable composition 235 is dispensed in bowl 210 of mold200 as discussed above with reference to FIG. 8. Lid 205 is then closedwith respect to bowl 210. As foamable composition 235 expands, gases areproduced and exit vent 700 via conduit 715 following the path of arrowsB. As foamable composition 235 fills the mold cavity, it reaches sensors720 in vent 700. When this happens, obstruction 710 is actuated to movein the direction of arrow C thereby effectively closing off escape ofgas via conduit 715—i.e., vent 700 is, for all intents and purposes,closed (FIG. 27).

Thereafter, obstruction 710 is moved in the direction of arrow D and theresulting foam part is demolded as discussed above. Alternatively, theresulting foam part can be demolded and then obstruction 710 can bemoved in the direction of arrow D in readiness for production of nextfoam part.

Thus, those of skill in the art will understand that vent 700 operatesas a relatively high capacity vent which has a sensor-actuated shot offsystem effectively sealing off escape of gas through the vent. In otherwords, vents 700 is operable between a first position in which itoperates as a high capacity vent and a second position in which the ventis effectively sealed.

An alternative to this approach is illustrated with respect to amodification of vent 700 to vent 700 a shown in FIGS. 23-24. In FIGS.23-24, the only significant change in vent 700 a is replacement ofobstruction 710 with obstruction 710 a.

Obstruction 710 a is similar to the obstruction appearing in vent 600described above and vent assembly 98 described in the Clark et. alpatents. Obstruction 710 a is actuated in the same manner as describedwith reference to obstruction 710 in FIGS. 25-28.

The resulting difference is that, unlike vent 700 illustrated in FIGS.25-28, vent 700 a illustrated in FIGS. 23-24 is operable between a firstposition in which the vent acts as a relatively high capacity, activevent and a second position in which the vent acts as low capacity,passive vent (i.e., in the second position the vent is not effectivelysealed off as it is in the embodiment described with reference to FIGS.25-28). The advantage of this approach is that the number of ventsneeded is reduced (as was the case with vent 700) since the vent inFIGS. 23-24 operates as a high capacity vent in the first positionwhile, on the other hand, the need to use precise timing to close offthe vent as shown in FIGS. 25-28 is alleviated with vent 700 a shown inFIGS. 23-24 since gas will continue to escape the vent even afterobstruction 705 is actuated to be in the second (low capacity, passivevent) position.

In some cases, this can obviate the need for sensors 720 where the samepart is being produced in the same mold. Specifically, a timing systemcan be used to move obstruction 710 a from its first (high capacity,active vent) position to its second (low capacity, passive vent)position.

With reference to FIG. 29, there is illustrated an enlarged view of aportion of foam part 240 (see also FIG. 10) comprising a portion ofnetwork 245 of foam ridge element formed by network 225 of grooves/slotsin mold 200. Further, an extruded section 250 is shown where foam curednear vent 220, 600, 700 and/or 700 a.

Advantageous features include a mold for producing molded articles, themold comprising a first mold and a second mold releasingly engageablebetween an open position and a closed position, the closed positiondefining a mold cavity, a surface of the mold cavity comprising at leastone groove connected to at least one vent, the at least one ventcomprising a passageway for gas to escape from the mold cavity. The ventmay be disposed in the first mold. The vent may be disposed in thesecond mold. The vent may be disposed in a partline between the firstmold and the second mold. The groove may be connected to a plurality ofvents. The plurality of vents may be disposed in the first mold. Theplurality of vents may be disposed in the second mold. The surface ofthe mold cavity may comprise a plurality of grooves. The surface of themold cavity may comprise a plurality of grooves disposed in the firstmold. The surface of the mold cavity may comprise a plurality of groovesdisposed in the second mold. The plurality of grooves may be arranged todefine a network of grooves. The plurality of grooves may be connectedto a plurality of vents. The groove may be disposed in a periphery ofthe first mold. The groove may be disposed in a periphery of the secondmold.

The first mold may comprise a lid, and the second mold may comprise abowl. The lid may comprise a contoured surface. The countered surfacemay comprise at least one peak region and one valley region. The groovemay be disposed in the at least one peak region. The groove may bedisposed in the at least one valley region. The groove may be disposedin the at least one peak region and the at least one valley region. Afirst plurality of grooves may be disposed in the at least one peakregion and a second plurality of grooves may be disposed in the at leastone valley region. The first plurality of grooves and the secondplurality of grooves may be interconnected. The first plurality ofgrooves and the second plurality of grooves may be isolated with respectto one another. The vent may be disposed in the at least one peakregion. The vent may be disposed in the at least one valley region. Afirst vent may be disposed in the at least one peak region and a secondvent may be disposed in the at least one valley region. The groove maycomprise an curvilinear cross-section. The groove may comprise asubstantially U-shaped cross-section. The groove may comprise asubstantially semi-circular cross-section. The groove may comprise arectilinear cross-section. The groove may comprise a substantiallyV-shaped cross-section. The groove may have a cross-section comprising apair of side walls interconnect by an apex portion. The side walls maybe parallel. The side walls may be non-parallel. The side walls may beangled with respect to one another. The side walls may be angled withrespect to one another to define an acute angle. The side walls may beangled with respect to one another to define an obtuse angle. The sidewalls may be angled with respect to one another to define right angle.The apex portion may be curved. The apex portion may be non-curved. Theapex portion may be pointed. The apex portion may be flat.

The groove may be dimensioned to have a depth and a width, the depthbeing greater than or equal to the width. The groove may be dimensionedto have a depth and a width, the depth being substantially equal to thewidth. The groove may be dimensioned to have a depth and a width, thedepth being greater than the width. The groove may be dimensioned tohave a depth of up to about 10 mm and a width of up to about 5 mm. Thegroove may be dimensioned to have a depth in the range of from about 3mm to about 10 mm and a width in the range of from about 0.5 mm to about5 mm. The groove may be dimensioned to have a depth in the range of fromabout 3 mm to about 7 mm and a width in the range of from about 1 mm toabout 4 mm. The groove may be dimensioned to have a depth in the rangeof from about 4 mm to about 6 mm and a width in the range of from about1.5 mm to about 2.5 mm. The groove may be dimensioned to have a depth ofabout 5 mm and a width of about 2 mm.

The vent may comprise a passageway and an obstruction in the passageway,the obstruction and the passageway combining to form at least oneopening. The vent may comprise a passageway and an obstruction in thepassageway, the obstruction and the passageway combining to form aplurality of openings. The opening may have a substantiallysegment-shaped cross-section. The passageway and the obstruction may bemovable between a retracted first position and an extended secondposition. The vent may have a greater capacity to allow gas to escapefrom the mold cavity in the first position than in the second position.The vent may comprise a passageway and an obstruction in the passageway,the passageway and the obstruction being movable with respect to oneanother between a first position in which gas may be allowed to escapefrom the mold cavity and a second position in which the vent may besubstantially closed with respect to escape of gas from the mold cavity.The vent may be disposed in a partline of first mold and the second moldto define an opening having maximum dimension and a minimum dimension.The minimum dimension may be in the range of from about 0.05 mm (0.002inches) to about 0.75 mm (0.030 inches). The minimum dimension may be inthe range of from about 0.13 mm (0.005 inches) to about 0.50 mm (0.020inches). The opening may be rectangular in cross-section.

Advantageous features also include a mold for producing molded articles,the mold comprising a lid and a bowl releasingly engageable to define amold cavity, the lid comprising: (i) a vent having a passageway for gasto escape from the mold cavity, and (ii) a plurality of groovesconnected to the vent. Advantageous features further include a devicefor producing molded articles, the device comprising a lid and a bowlreleasingly engageable between an open position and a closed position,the closed position defining a mold cavity, at least one of the lid andthe bowl comprising: (i) a plurality of vents, each vent having apassageway for gas to escape from the mold cavity, and (ii) a pluralityof interconnected grooves arranged to be in fluid communication with theplurality of vents. Advantageous features further include a process forproducing a molded part comprising the steps of: (i) dispensing amoldable composition in one of the first mold and the second mold; (ii)translating gas in the mold cavity to the least one groove, (iii)translating gas from the at least one groove to the passageway of thevent; (iv) substantially filling the mold cavity with the moldablecomposition, and (v) allowing gas to escape from the passageway of thevent to an exterior of the mold. The mold may be in the open positionduring Step (i) and in the closed position during Step (iv).

Advantageous features may also include a process for producing a moldedpart comprising the steps of: (i) dispensing a moldable composition inthe bowl; (ii) translating gas in the mold cavity to the plurality ofgrooves, (iii) translating gas from the plurality of grooves to thepassageway of the vent; (iv) substantially filling the mold cavity withthe moldable composition, and (v) allowing gas to escape from thepassageway of the vent to an exterior of the mold. The mold may be in anopen position during Step (i) and in a closed position during Step (iv).Advantageous features may further include a process for producing amolded part comprising the steps of: (i) dispensing a moldablecomposition in the bowl; (ii) translating gas in the mold cavity to theplurality of interconnected grooves, (iii) translating gas from theplurality of interconnected grooves to the plurality of vents; (iv)substantially filling the mold cavity with the moldable composition, and(v) allowing gas to escape from the plurality of vents to an exterior ofthe device. The mold may be in the open position during Step (i) and inthe closed position during Step (iv). The process may comprisedispensing a liquid foamable composition. The process may comprisedispensing a liquid foamable polyurethane composition.

While this invention has been described with reference to illustrativeembodiments and examples, the description is not intended to beconstrued in a limiting sense. Thus, various modifications of theillustrative embodiments, as well as other embodiments of the invention,will be apparent to persons skilled in the art upon reference to thisdescription. For example, it is possible to modify lid 205 of mold 200to modify the shape and/or dimension of extruded portion 250 inresulting foam part 240. Alternatively, it is possible to modify lid 205of mold 200 to eliminate production of extruded portion 250 in resultingfoam part 240. Still further, it is possible to modify interconnectionof vents 220, 600, 700 and/or 700 a to lid 205 such that the distalportion of vents 220, 600, 700 and/or 700 a is substantially flush withthe mold cavity surface of lid 205. Still further, it is possible tomodify the network of grooves/slots 225 to have a different design. Forexample, it is possible to design a network of grooves/slots to includea diamond-shaped repeating pattern, optionally including a series ofsubstantially parallel grooves/slots wherein each groove/slot bisects arow of diamonds in the repeating pattern. Alternatively, it is possibleto design a network of grooves/slots to include a series ofsubstantially parallel grooves/slots (i.e., in a so-called radiator typearrangement with a spacing between adjacent pairs of grooves/slots inthe range of from about 2 cm to about 5 cm). In each case, it ispreferred to included a perimeter groove/slot connected to the networkof grooves/slots, more preferably connected to each groove/slot in thenetwork. It is therefore contemplated that the appended claims willcover any such modifications or embodiments.

All publications, patents and patent applications referred to herein areincorporated by reference in their entirety to the same extent as ifeach individual publication, patent or patent application wasspecifically and individually indicated to be incorporated by referencein its entirety.

1. A mold for producing molded articles, the mold comprising a firstmold and a second mold releasingly engageable between an open positionand a closed position, the closed position defining a mold cavity, asurface of the mold cavity comprising at least one vent; wherein thevent comprises an opening and an obstruction, the obstruction beingmovable with respect to the opening between a first position in whichgas is allowed to escape from the mold cavity via the opening and asecond position in which the obstruction blocks the opening.
 2. The molddefined in claim 1, further comprising a sensor for sensing the presenceof a predetermined amount of moldable material in the mold cavity, thesensor configured to actuate the obstruction from the first position tothe second position when the predetermined amount of moldable materialis detected.
 3. The mold defined in claim 1, further comprising a sensorfor sensing the presence of a predetermined level of moldable materialin the mold cavity, the sensor configured to actuate the obstructionfrom the first position to the second position when the predeterminedamount of moldable material is detected.
 4. The mold defined in any oneof claims 2-3, wherein the sensor comprises an optical sensor.
 5. Themold defined in any one of claims 2-3, wherein the sensor comprises aninfrared sensor.
 6. The mold defined in any one of claims 2-3, whereinthe sensor comprises an acoustical sensor.
 7. The mold defined in anyone of claims 2-3, wherein the sensor comprises capacitance sensor. 8.The mold defined in any one of claims 2-7, wherein the sensor comprisesa pair of sensor elements.
 9. The mold defined in any one of claims 2-7,wherein the sensor comprises a pair of substantially opposed sensorelements.
 10. The mold defined in any one of claims 2-9, wherein theobstruction is reversibly movable in a passageway.
 11. The mold definedin claim 10, wherein the opening is disposed in a surface of thepassageway.
 12. The mold defined in any one of claims 10-11, wherein theobstruction and the passageway combine to form at least one opening. 13.The mold defined in any one of claims 10-11, wherein the obstruction andthe passageway combine to form a plurality of openings.
 14. The molddefined in any one of claims 12-13, wherein the at least one opening hasa substantially segment-shaped cross-section.